The present invention relates generally to displays having a plurality of individually controllable pixels. More specifically, the invention relates to displays having pixels which respond variably over the area of each pixel in response to an applied electrical field directed through each pixel.
Typically the resolution of a display is improved by reducing the size of the pixels and increasing the number of pixels making up the display. Typical high resolution displays have on the order of 1000 rows and 1000 columns of pixels resulting in a total of on the order of 1,000,000 pixels. Also, conventional displays provide gray scale (monochrome or color) by allowing each individual pixel making up the display to be operated at one of a plurality of discrete gray scale levels during any given frame or by time multiplexing binary response pixels to produce time averaged gray scale. As the number of pixels are increased to improve resolution, and as the number of gray scale levels are increased to improve the quality of the image, the amount of data that must be transferred to the display for each given frame is significantly increased requiring more complex controllers and pixel addressing schemes to operated the display.
Most images are made up of gray levels and/or other colors that vary gradually as a function of position. Therefore, to provide a relatively smooth transition, for example from a light gray scale to a dark gray scale, the pixels in the area of the display where the transition is being made are controlled such that each consecutive adjacent pixel has a slightly darker gray scale than the previous pixel. Because of this incremental approach, it takes a large number of pixels (i.e. a high density of pixels) to provide a smooth transition.
3D displays are currently being developed which use coherent, in phase light to illuminate or back light a display. Each pixel of the display modulates the phase of the light passing through that pixel in a controlled way which causes the light passing through that pixel to be out of phase with the light passing through other near by pixels. This approach to providing a 3D display is referred to as phase modulation to produce wave front reconstruction. The differences in the phase of the light passing through the various pixels provides visual queues that cause the image created by the display to appear to be a three dimensional image. This approach to providing a 3D display is described in detail in an article written by P. St. Hilaire, S. A. Benton, and M. Lucente entitled "Synthetic Aperture Holography: A Novel Approach to Three-Dimensional Displays" published in the Journal of the Optical Society of America, A, 9, 1969-1977 (1992), which is incorporated herein by reference.
One of the most challenging aspects of developing 3D wave front reconstructing displays is that the pixels must be sufficiently small for holography. Putting it differently, the pixel pitch must be sufficiently small for the Fresnel diffraction cone to provide the desired field of view or viewing angle. This requires that the spatial extent of each pixel is limited to approximately the wavelength of the light being used by the display divided by the side of the desired viewing angle. This diffraction criterion is well known to those skilled in the art and hence will not be described in more detail herein.
For visible light and a viewing angle of approximately fifteen degrees, the display would require a pixel pitch of approximately 2 .mu.m irrespective of the overall size of the display. A pixel pitch of 2 .mu.m is extremely difficult to achieve in a display, and even for a very small display such as a 1 cm.sup.2 display, this pixel pitch would result in a display having approximately 5000 rows and 5000 columns of pixels. This extremely high pixel count creates a substantial information transfer problem. As the size of the display is increased, this problem further increases since the pixel pitch cannot be reduced.
The present invention provides a display having individually controllable pixels, each of which responds variably over the area of the pixel. As will be seen, using the present invention in a conventional two dimensional display, this individual controllably variable response of each pixel relaxes the pixel pitch requirement necessary to provide a given resolution for displaying images having varying gray scales in the image. That is, the pixel pitch does not have to be as small as it would have to be in conventional displays to provide the same resolution. In a phase modulating type 3D display as described above, the individual controllably variable response pixels may be used to variably modulate the phase of the light over the area of each pixel. Since the present invention allows the light to be variably phase modulated over the area of each pixel, the phase interference necessary to provide the 3D effect is provided within each pixel. This allows a phase interference type 3D display to be built without being limited to a pixel pitch dictated by the wavelength and the viewing angle as described above.